This invention relates generally to micro lead frame plastic (MLP) packages, and more particularly, to a connection arrangement for MLP packages.
At RF, microwave and millimeter-wave frequencies, plastic packages are preferred because of the low cost and ease of manufacturing. For example, lead frames are much lower in cost compared to substrates used in Ball Grid Array packages. However, as the operating frequency increases, the effect of the package on the component/circuit overall RF performance becomes increasingly important. In addition to good electrical characteristics, when designing a package, it is also important to consider thermal dissipation path, space requirements or limitations, environmental protection and component reliability.
The use of plastic packages is currently limited to low frequency applications, for example, applications with a maximum frequency of about 5 GHz. This is due mainly to the parasitics (e.g., large inductance) associated with bond wire discontinuity of the chip-package-motherboard transition. These parasitics are particularly severe at higher frequencies, such as, for example, at 24 GHz. The parasitics are also caused by the use of a paddle and ground pads that are not connected and thereby fail to provide a continuity of ground, particularly at the higher frequencies. These parasitics result in high insertion loss, poor impedance matching and a large response over the required frequency band. The RF behavior of the chip-package-motherboard transition also results in a large power drop off with frequency.
The parasitic effects are sometimes overcome by including additional matching stubs on, for example, the Monolithic Microwave Integrated Circuit (MMIC) chip itself. However, as the space on the chip is often very limited, this on-chip matching can be complex and can be very expensive to implement. Moreover, using the matching stubs, the frequency bandwidth is very limited, making these configurations unacceptable for ultra broadband systems such as High Resolution Radar (HRR). Other solutions are also known and include using the parasitics for matching the amplifiers on the chip. However, these solutions also can be difficult to implement.
Flip-chip versions of MLP packages are also known for addressing the operating frequency problems. In these packages, a bumped die is flipped onto a lead frame paddle and then molded using a standard plastic package assembly process. Flip chip designs reduce signal inductance because the interconnect is much shorter when compared to a bond wire (e.g., 0.1 mm versus 1 mm). However, the manufacturing processes for such flip chip processes may not be satisfactory for mass production in large quantities.
Thus, known MLP packages either do not operate satisfactorily at higher frequencies or are complex and expensive to implement.